Yeah, I was wondering. We say "french fries" but the french don't call them french fries, and we talk about "french toast" but the french don't call it french toast. We say "bolognese sauce" but in bologna they just say "ragu'" - and that's for things that are actually made and eaten in these places. Let's not get into "Italian dressing" which is not even eaten in Italy - they don't "make" "dressing" here, but just pour oil and vinegar on the salad and mix well with the greens. Only one person i know here makes "dressing" in the sense of mixing the ingredients before putting on the salad, and she's french and does a nice "vinaigrette" and doesn't call it "french"..
So I wonder if in Nice they just make salad, and if "salade nicoise" is not just a name used by people outside of Nice for this type of salad. Which would account for the variety of ingredients, the arrangement done nicely in a flat dish, etc. I mean, apart from restaurants in Nice, (which would probably have incorporated "nicoise" into their menu because it is a resort town), I wonder if the locals don;t just call it "salade"
I wonder, at this point, if its southern counterpart, "insalata caprese" is just a salad people will make, among others, in capri and the naples area, and tourists from other parts of italy on vacation there loved it and referred to it as caprese. In Naples do they call pizza with tomato, mozzarella and anchovies "pizza napolitana" or just pizza.
In Boston when i was a kid, "boston baked beans" were just "baked bean" - and only now, with greater variety in stores and more people living in different cities than they were born in, do they call them "BOSTON baked beans" even in boston, but not all the time.
Sorry, this is a linguistic and cultural digression and doesn;t have much to do with salads - but that's what's fun about these threads!